This invention relates to an improved process for the preparation of poly(trimethylene terephthalate) from 1,3-propanediol and a C1-C4 dialkyl terephthalate in which the levels of units from di(1,3-propylene glycol) (xe2x80x9cDPGxe2x80x9d) in the poly(trimethylene terephthalate) are reduced.
Preparation of poly(trimethylene terephthalate) (3GT) polyester resins by (a) the transesterification of a C1-C4 dialkyl ester of terephthalic acid with 1,3-propanediol, or by the esterification of terephthalic acid with 1,3-propanediol, followed by (b) polycondensation is well known in the art.
Generally, in the transesterification reaction, a C1-C4 dialkyl ester of terephthalic acid and 1,3-propanediol arc reacted in the presence of a transesterification catalyst at elevated temperature and atmospheric pressure to form bis-(3-hydroxypropyl)terephthalate monomer, along with small amounts of oligomer and C1-C4 monoalcohol byproduct. In the esterification reaction, terephthalic acid (TPA) and 1,3-propanediol are reacted in the optional presence of an esterification catalyst at elevated temperature and at atmospheric or superatmospheric pressure to form bis-(3-hydroxypropyl)terephthalate monomer, along with small amounts of oligomer and water byproduct. The bis-(3-hydroxypropyl)terephthalate monomer and any oligomer can then be polymerized at higher temperature under reduced pressure in the presence of a polycondensation catalyst to form the desired resin.
During the process for the preparation of 3GT (transesterification, esterification and polycondensation reactions), di(1,3-propylene glycol) can be formed from intermolecular dehydration of 1,3-propanediol. This di(1,3-propylene glycol) can be incorporated into the 3GT polymer chain which affects the properties of the resulting polymer, with respect to, for example, melting temperature, glass transition temperature, crystallinity, density, dyeablity, processability, etc. The effects of the analogous impurity, diethylene glycol (DEG), on poly(ethylene terephthalate) (PET) polymer properties are well documented in the literature. For commercial grade PET the DEG levels are usually around 2-4 mol %.
Processes for the preparation of polyesters, including 3GT, have been disclosed in many patents. Some disclose use of tin and titanium catalysts.
U.S. Pat. No. 2,465,319 mentions many types of catalysts including tin. Research Disclosure 28368 (November 1987) discloses preparation of poly(alkylene 2,6-napthalenedicarboxylate) polyesters using titanium alkoxides and dibutyl tin dilaurate, etc.
U.S. Pat. Nos. 3,350,871 and 3,671,379, and UK Patent Specification No. 1,075,689, Example 1, show preparation of poly(trimethylene terephthalate) from dimethyl terephthalate and trimethylene glycol using a catalyst prepared by dissolving 2.5 grams of sodium in 300 ml of n-butanol, adding 37 grams of tetrabutyl titanate, and diluting to 500 ml with n-butanol. Titanium dioxide is added as a delusterant.
U.S. Pat. No. 4,166,896 describes dibutyl tin oxide as a catalyst. U.S. Pat. No. 4,611,049 describes a process for producing an aromatic polyester using an organometallic catalyst selected from the group consisting of organotitanium compounds and organotin compounds, and at least one promoter selected from the group consisting of organic sulfonic acids and aliphatic carboxylic acids. Tetrabutyl titanate, tetraisopropyl titanate, dibutyl tin oxide and butylhydroxytin oxide are preferred.
U.S. Pat. No. 5,340,909 describes preparation of poly(1,3-propylene terephthalate) using tin and titanium catalysts. Catalysts mentioned include tetrabutyl titanate, tetraisopropyl titanate, butylstannoic acid, butyltin tris (2-ethylhexoate), stannous octoate, dibutyltin tris(2-etholhexoate), stannous octoate, dibutyltin oxide and methylene bis(methyltin oxide). Tetrabutyl titanate is used in both control and demonstration examples.
U.S. Pat. No. 5,663,281 describes a process for preparing polyester polymers. At column 6 it states that (trans)esterification reactions from 1,4-butanediol using tetrabutyl titanate are satisfactory, but risk forming undesirable by-products, whereas with 1,3-propylene glycol the risk of forming undesirable by-products using tetraalkyl titanates as catalyst is not as great and, thus, xe2x80x9cmore traditionalxe2x80x9d catalysts such as tetrabutyl titanate and antimony oxide can be used. Monobutyl tin oxide is used to catalyze 1,4-butanediol reactions.
U.S. Pat. No. 5,798,433 discloses a method of synthesizing polypropylene terephthalate using 30-200 ppm titanium in the form of an inorganic esterification catalyst containing at least 50 mole % TiO2 precipitate, blocking the esterification catalyst after esterification by adding 10-100 ppm phosphorus in the form of a phosphorus-oxygen compound, and then performing precondensation and polycondensation in the presence of 100-300 ppm antimony. Table 1 shows a comparative example using titanium tetrabutylate as an esterification catalyst with antimony triacetate as a polycondensation catalyst.
U.S. Pat. No. 5,872,204 describes preparation of poly(1,3-propylene terephthalate) using ethylene glycol titanate as an esterification catalyst and polymerizing the resultant monomer in the presence of antimony acetate. At column 2 it is stated that ethylene glycol titanate does not hydrate, whereas tetrabutyl titanate does. The examples show use of ethylene glycol titanate, whereas comparative example 1 may have been directed to use of tetrabutyl titanate (compare column 12, lines 46 and 63).
None of these references mention DPG formation, specify DPG levels, nor cite the impact of DPG content on polymer end use properties, and none disclose methods to minimize DPG generation during the polymer preparation processes.
U.S. Pat. No. 5,8365,424 described preparation of polyesters containing low levels of diethylene glycol wherein the reaction is carried out without a titanium catalyst.
U.S. Pat. No. 6,043,335 describes preparation of polyethylene and polybutylene terephthalates (which are stated to not have high levels of undesirable by-products) using a catalyst composition comprising a combination of a titanium-based compound, a zirconium-based compound and a phosphate-forming compound.
WO 98/23662 states that the condensation polymerization of polytrimethylene terephthalate xe2x80x9cusually generates as much as about 4 mole percent of the bis(3-hydroxypropyl) ether which, in effect, becomes a comonomer and is incorporated into the polyester chain.xe2x80x9d
EP 1 016 692 and 1 016 741 describe polyester resin and fibers produced with no more than 2 weight % bis(3-hydroxypropyl) ether (DPG derived repeating unit). These documents describe use of metal catalysts such as titanium alkoxides (e.g., titanium tetrabutoxide or titanium tetraisopropoxide), antimony acetate or antimony trioxide. The preferred ester exchange catalysts are stated to be calcium acetate, magnesium acetate, zinc acetate and titanium acetate. In addition, they describe titanium, tin or antimony polycondensation catalysts, preferring titanium tetrabutoxide.
All of the aforementioned documents are incorporated herein by reference.
This invention is directed to improved process for preparing 3GT polyester having high strength, excellent elastic recovery, easy dyeability and containing low levels of DPG, and the resultant poly(trimethylene terephthalate) polyester.
Specifically, the invention is directed to a process of preparing poly(trimethylene terephthalate) containing less than 2.0 mole % of DPG. The process comprises:
(a) providing a molar amount of 1,3-propanediol:C1 to C4 dialkyl ester of terephthalic acid of 1.2:1 to 1.9:1;
(b) reacting the 1,3-propanediol with the C1 to C4 dialkyl ester of terephthalic acid to form bis(3-hydroxypropyl)terephthalate monomer in the presence of 10-100 ppm (as titanium metal) of an organic titanate catalyst, by weight of the poly(trimethylene terephthalate); and
(c) polymerizing the bis(3-hydroxypropyl)terephthalate monomer to obtain the poly(trimethylene terephthalate).
Preferably, the molar amount is 1.4:1 to 1.8:1.
Preferably the catalyst comprises one or more titanium tetrahydrocarbyloxide catalyst, most preferably tetraisopropyl titanate.
Preferably the polymerizing the bis(3-hydroxypropyl)terephthalate monomer is carried out using an effective amount of the organic titanate catalyst, most preferably using 0-100 ppm (as titanium metal) of the organic titanate catalyst (by weight of the poly(trimethylene terephthalate)).
Preferably the process is carried out so that the product polyester contains less than 1 mole % DPG.
The invention is also directed to poly(trimethylene terephthalate) produced by the process.
Other and further objects, features, and advantages of the present invention will appear more fully from the following description.
This invention relates to an improved process for the preparation of poly(trimethylene terephthalate) from 1,3-propanediol (xe2x80x9cPDOxe2x80x9d) and a C1-C4 dialkyl terephthalate in which the levels of units from di(1,3-propylene glycol) (xe2x80x9cDPGxe2x80x9d) (also known as xe2x80x9cbis(3-hydroxypropyl) etherxe2x80x9d or xe2x80x9cBPExe2x80x9d) are reduced. Such units have also been referred to as xe2x80x9ccopolymerized BPExe2x80x9d. These units in the poly(trimethylene terephthalate) polymer actually have the formula
xe2x80x94(OCH2CH2CH2OCH2CH2CH2O)xe2x80x94,
but are called xe2x80x9cDPGxe2x80x9d herein for convenience.
The most preferred polymer is poly(trimethylene terephthalate). Also preferred are blends and copolymers of poly(trimethylene terephthalate). The polymer of the invention contains preferably about 80% or more of poly(trimethylene terephthalate) in mole percentage. It may be modified with up to 20 mole percent of polyesters made from other diols or diacids. The other diacids include isophthalic acid, 1,4-cyclohexane dicarboxylic acid, 2,6-naphthalene dicarboxylic acid, 1,3-cyclohexane dicarboxylic acid, succinic acid, glutaric acid, adipic acid, sebacic acid, 1,12-dodecane dioic acid, and the derivatives thereof such as the dimethyl, diethyl, or dipropyl esters of these dicarboxylic acids. The other diols include ethylene glycol, 1,4-butane diol, 1,2-propanediol, diethylene glycol, triethylene glycol, 1,3-butane diol, 1,5-pentane diol, 1,6-hexane diol, 1,2-, 1,3- and 1,4-cyclohexane dimethanol, and the longer chain diols and polyols made by the reaction product of diols or polyols with alkylene oxides.
The 3GT polymers of the invention have less than 2 mole % DPG, and most preferably less than 1 mole %.
The intrinsic viscosity of the polymers of the invention are in the range of 0.4-2.0 dl/g, preferably in the range of 0.6-2.0 dl/g and most preferably in the range of 0.7-2.0 dl/g.
To achieve the object of the present invention, 3GT polyester is prepared utilizing specific ratios of reactants and in the presence of specific catalyst(s).
The mole ratio (PDO: C1 to C4 dialkyl esters of terephthalic acid) of starting materials is 1.9:1 or less, preferably 1.8:1 or less, and is preferably 1.2:1 or higher, most preferably 1.4:1 or higher. Operation at higher molar ratios than 1.9:1 leads to increased amounts of DPCJ formed. Generally, in this embodiment bis(3-hydroxypropyl)terephthalate monomer is prepared using 10-100 ppm titanate catalyst (as titanium metal), by weight of the poly(trimethylene terephthalate).
Of the various C1 to C4 dialkyl esters of terephthalic acid, dimethyl terephthalate (DMT) is preferred.
The preferred titanium compounds are organic titanate compounds. Titanium tetrahydrocarbyloxides, also referred to as tetraalkyl titanates herein, are presently most preferred organic titanium compounds because they are readily available and effective. Examples of suitable titanium tetrahydrocarbyloxide compounds include those expressed by the general formula Ti(OR)4 where each R is individually selected from an alkyl or aryl radical containing from 1 to about 30, preferably 2 to about 18, and most preferably 2 to 12 carbon atoms per radical and each R can be the same or different. Titanium tetrahydrocarbyloxides in which the hydrocarboxyl group contains from 2 to about 12 carbon atoms per radical which is a linear or branched alkyl radical are most preferred because they are relatively inexpensive, more readily available, and effective in forming the solution. Suitable titanium tetrahydrocarbyloxides include, but are not limited to, titanium tetraethoxide, titanium tetrapropoxide, titanium tetraisopropoxide (also known as xe2x80x9ctetraisopropyl titanatexe2x80x9d), titanium tetra-n-butoxide, titanium tetrahexoxide, titanium tetra 2-ethylhexoxide, titanium tetraoctoxide, and combinations of two or more thereof.
Titanium tetrahydrocarbyloxides suitable for use in the present invention can be produced by, for example, mixing titanium tetrachloride and an alcohol in the presence of a base, such as ammonia, to form the titanium tetracarbyloxide or tetraalkyl titanate. The alcohol can be ethanol, n-propanol, isopropanol, n-butanol, or isobutanol. Titanium tetrahydrocarbyloxides thus produced can be recovered by first removing by-product ammonium chloride by any means known to one skilled in the art such as filtration followed by distilling the titanium tetrahydrocarbyloxides from the reaction mixture. This process can be carried out at a temperature in the range of from about 0 to about 150xc2x0 C. Titanates having longer alkyl groups can also be produced by transesterification of those having R groups up to C4 with alcohols having more than 4 carbon atoms per molecule.
The preferred transesterification catalyst in the process of the present invention is tetraisopropyl titanate (TFPT). Tetraisopropyl titanate is commercially available as TYZOR(copyright) TPT from E.I. du Pont de Nemours and Company, Wilmington, Del., U.S.A. (xe2x80x9cDuPontxe2x80x9d).
After the initial stage of the 3GT preparation process, di(1,3-propylene glycol) formation, the second step, polycondensation (step c) to finished polymer is carried out in the presence of any of the customarily employed polycondensation catalysts. Organic titanates are preferred. Tetraisopropyl titanate is most preferred.
Polycondensation is preferably carried out using 10-100 ppm titanate catalyst (as titanium metal), by weight of the poly(trimethylene terephthalate).
It is believed that the use of tetraisopropyl titanate (TPT) as both the transesterification catalyst and polycondensation catalyst leads to shortened reaction times versus the use of tetrabutyl titanate (TBT).
The transesterification is customarily carried out at atmospheric pressure in the temperature range of from 150-250xc2x0 C. A preferred temperature range is from 200-220xc2x0 C.
The polycondensation reaction is customarily carried out at reduced pressures (below 1.0 mmHg) and at temperatures of from 230-280xc2x0 C. Temperatures from 240-260xc2x0 C. are preferred.
Additives known in the art such as antioxidants, UV stabilizers, pigments (e.g., TiO2, etc.), flame retardants, antistats, dyes, and compounds that enhance the process, etc., may be used with this invention.
Use of a phosphate or a phosphate-forming compound, such as described in EP 1 016 741, EP 1 016 692 and U.S. Pat. No. 5,798,433, all of which are incorporated herein by reference, is not desirable with this invention.
Use of a promoter i(organic sulfonic acids and aliphatic carboxylic acids) such as described in U.S. Pat. No. 4,611,049, incorporated herein by reference, is unnecessary, and probably undesirable with this invention.
Use of an aromatic organosphosphite and hindered phenol such as described in U.S. Pat. No. 6,043,335, incorporated herein by reference, is also unnecessary.
The polyesters of this invention have excellent crystallinity. The lower levels of DPG result in higher strength. These polyesters are useful in many of the end uses described in the art, particularly in fibers and yarns where they provide excellent strength. They are also useful in engineering resins, films and nonwovens, etc.